I have a rice cooker. I love my rice cooker. Put in rice, water, and salt, slap the lid on, and turn the switch to Cook and concentrate on preparing the rest of the meal - and about twenty minutes later, the switch goes PING! and switches back to Keep Warm. The rice inside has never turned out to be anything less than perfectly cooked.
But what mechanism drives this magic appliance? How does it now when the rice is ready? I don’t think this is as simple as a timer, since it copes with a little too much or a little too little water, but I can’t figure out what else it could be.